I do love Charlie as a nn for Charlotte. While I hate boy's names on girls, Charlie is a historically legitimate (and phonetically logical) nickname for Charlotte. Unfortunately, I don't think Charlie really works as a short form of any other name. Charlotte is the feminized form of Charles, which is why Charlie makes sense as a short form. For any other name, it just feels random and doesn't make much sense.

How about Charianne? My friend is named Charianne and she goes by that, but I don't see why Charlie couldn't work! Same first 4 letters. It is a different sound, but I think it could work. Or maybe Sher - like the famous singer? Or any names that start with Cher? Cheryl? Cherisse? These are more of a stretch, but I don't see why it couldn't work!